Larval Fish and Egg Key - Freshwater

Resources:For full bibliographic references: LarvalfishID Reference Shelf

NOTE: Meristics at the family level may not be indicative of all species within that family, especially species outside of the key’s geographic region or for families that have limited data available. In addition, because some species have different features at different sizes (e.g., coiled gut at 8mm and s-shaped gut at 19mm), the fact sheets will show all possible options and do not differentiate by size.

Gymnocephalus cernua (Ruffle)

General information
Where found: Lake Superior
Native or non-native species: Non-native

Egg (spawning to hatching)

Appearance and features
Egg shape: Round
Egg attachment structure: Absent
Type: Demersal
Buoyancy: Buoyant or semibuoyant
Cleavage: Meroblastic

Oil globule diagnostics
Oil globule (presence): Present
Frequency/number: One
Oil globule location in yolk sac: Anteriorly located

Yolk Sac Larvae - YSL (hatching to complete absorption of yolk)

Appearance and features (body)
Body shape: Elongate, not eel-shaped
Gill openings on each side: Single
Location of anus: Mid-body
Intestine/Gut form: Straight / uncoiled (may be curved but not coiled or folded back on itself)
Spiral valve: Absent
Swim bladder (presence): Absent (or not yet filled or obscured by tissues) - not visibly obvious

Appearance and features (fins and finfold)
Pectoral fins: Present
Adipose fin: Absent
Caudal fin type and shape: Homocercal (upper lobe symmetrical to lower), caudal fin rounded or truncated
Preanal finfold: Present, separated from rest of ventral finfold

Appearance and features (head and mouth)
Head size: Small (< 15% TL) or medium (15-20% TL)
Eye (relative size): Moderate to large (> 5% TL), small (1-5% TL)
Snout shape: Short, round or squared off and blunt
Adhesive disc or organ on snout: Absent
Chin barbels: Absent or not well developed
Gular plate between lower jaws: Absent
Opercular spine(s): Absent

Appearance and features (yolk sac)
Yolk sac shape: Round or nearly so (spherical)
Position of yolk sac: Anus far posterior to yolk sac
Presence of yolk: Present

Oil globule diagnostics
Oil globule (presence): Present
Frequency/number: Single
Appearance: Large
Position of oil globule(s) in yolk sac: Anterior

Meristics
Total Length (TL) of yolk-sac larvae (mm): 3.6-6.5 mm
Total length of recently hatched larvae (mm): 3.6-4.8 mm

Myomeres
Total myomeres: 35-49

Morphometry (as % of Total Length TL)
Preanal length: 49-50 %

Pigmentation (general)
Eyes: Pigmented
Eye pigmentation details: Darkly pigmented

Larvae (complete absorption of yolk to development of full complement of adult fin rays and absorption of finfold)

Appearance and features
Body shape: Elongate, not eel-shaped
Gill openings on each side / gill characteristics: Single
Anus (vent) location: Mid-body
Intestine/Gut form: Straight / uncoiled

Appearance and features (fins)
Adipose fin: Absent, no adipose fin or position not evident in finfold
Pelvic spine (presence): Present
Caudal fin and peduncle: Homocercal or isocercal tail (both lobes symmetrical) or caudal fin rounded or square, Present, caudal fin rays visible
Pectoral fins: Present
Pectoral fins (description): Pectoral fins well developed or large pectoral fins
Median (dorsal and/or caudal) fins: Spinous and soft-rayed, Median fins/finfolds show distinct separation
Preanal finfold: Present, separated from rest of ventral finfold by vent
Anal fin rays (presence): Present, anal fin rays and/or spines visible
Dorsal fin (description): Spinous dorsal separate from soft dorsal fin

Appearance and features (head and mouth)
Snout length: Snout short (< 10 % of Total Length TL)
Chin barbels: Absent or not well developed
Presence of mouth: Present, formed, or functional (postion as in adult)

Meristics
Total length (mm): (6.0-)7.0-11.0(-12.0) mm
Number of dorsal fins: Double

Myomeres
Preanal myomere count: 17-20
Postanal myomere count: 18-21
Total myomere count: 36-39

Morphometry (as % of Total Length TL)
Preanal length: 51-52 %
Standard length: 95-96 %

Pigmentation (general)
Body: Pigmented
Body (general regions with pigment): Pigment on venter
Body areas without pigment: No midlateral stripe/band or stripe indistinct, no parr marks (round to vertically elongate) or vertical bars on lateral surface
Eyes: Pigmented